1. Field
The present disclosure relates to a magnetic pole position detection device that, on the basis of a current draw-in scheme, detects an amount of deviation between an origin of a magnetic pole position of a permanent magnet that makes up a rotor of a permanent magnet-type synchronous motor, and an origin (reference position) of an output signal of a magnetic pole position sensor, and that detects a true magnetic pole position on the basis of the amount of deviation.
2. Related Art
FIG. 1 is a configuration diagram of a driving system in which a permanent magnet-type synchronous motor is driven by an inverter. FIG. 1 includes a permanent magnet-type synchronous motor (PMSM) 1, a magnetic pole position sensor 2, such as an encoder, attached to a rotor shaft of the synchronous motor 1, an inverter control device 3 to which a speed command value n* is inputted, and a PWM inverter 4. In this driving system, speed control and position control by the synchronous motor 1 are performed by feeding back, to the inverter control device 3, a magnetic pole position θ of the rotor (permanent magnet) of the synchronous motor 1 as detected by the magnetic pole position sensor 2, and generating a driving signal for a semiconductor switching element of the inverter 4.
FIG. 2 is a block diagram illustrating the specific configuration of the inverter control device 3 of FIG. 1, the purpose of the inverter control device 3 being herein to drive the synchronous motor 1 according to so-called vector control. In FIG. 2, a subtractor 30 works out a deviation between a speed command value n* and a speed detected value n, and a speed regulator 31 computes a torque command value Trq* such that the deviation becomes zero. A current command calculator 32 computes, on the basis of the torque command value Trq*, a d-axis current command value Id* and a q-axis current command value Iq* being components that are mutually orthogonal in d-q rotating coordinates. As is known, the d-axis is a virtual axis of control along a magnetic flux axis of the permanent magnets that make up the rotor of the synchronous motor 1. The q-axis is an axis orthogonal to the d-axis. Furthermore, a differential calculator 39 computes the speed detected value n through differentiation of a magnetic pole position (angle) θ of the rotor.
Meanwhile, output currents Iv, Iw of the inverter 4 are detected by current detectors 42, 43, and the detected values are inputted to a coordinate converter (three-phase/two-phase converter) 38. The coordinate converter 38 converts three-phase currents Iu, Iv, Iw, including the output currents Iv, Iw, to a d-axis current detected value Id and a q-axis current detected value Iq of two phases, using the magnetic pole position θ. A current regulator 35 operates to generate a d-axis voltage command value Vd* such that the deviation between the d-axis current command value Id* and the d-axis current detected value Id worked out by the subtractor 33, becomes zero. A current regulator 36 operates to generate a q-axis voltage command value Vq* such that the deviation between the q-axis current command value Iq* and the q-axis current detected value Iq, worked out by the subtractor 34, becomes zero.
A coordinate converter (two-phase/three-phase converter) 37 converts the d-axis voltage command value Vd* and the q-axis voltage command value Vq* to three-phase voltage command values Vu*, Vv*, Vw*, using the magnetic pole position θ. Through an on-off operation of an internal semiconductor switching element, the PWM inverter 4 outputs a three-phase AC voltage corresponding to the voltage command values Vu*, Vv*, Vw*, to drive thereby the synchronous motor 1.
In the above configuration, absolute position information on the rotor of the synchronous motor 1 is obtained at the coordinate converters 37, 38 on the basis of the magnetic pole position θ as detected by the magnetic pole position sensor 2. However, it is difficult to accurately match the origin of the magnetic pole position of the rotor and the origin of the output signal of the magnetic pole position sensor 2, due to requirements in terms of simplifying to some extent the assembly operation of the motor, and also due to precision and cost constraints. Therefore, the amount of deviation between the origin of the magnetic pole position and the origin of the output signal of the magnetic pole position sensor 2, i.e. the amount of deviation of the magnetic pole position as viewed from the output side of the magnetic pole position sensor 2, is ordinarily detected manually or automatically, before the synchronous motor 1 is operated for the first time, and is stored in a memory, whereupon this amount of deviation is corrected according to a control computation algorithm.
For example, the invention disclosed in Japanese Patent Application Publication No. H11-252972 (for instance, paragraphs [0006], [0007], FIG. 2) is a known instance of a technology that involves detecting the amount of deviation of a magnetic pole position in accordance with a so-called current draw-in scheme, and operating a permanent magnet-type synchronous motor, during normal operation, using a magnetic pole position corrected by the amount of deviation. FIG. 7 is a flowchart illustrating the magnetic pole position detection method described in this patent application publication.
In FIG. 7, firstly, a magnetic pole position (phase) θ0 is virtually set to 0°, and DC current (d-axis current Id) is caused to flow, in the d-axial direction, through armature windings of the permanent magnet-type synchronous motor (step S1). Rotation torque is generated thereupon, since the direction of the magnetic flux by the d-axis current Id and the direction of the magnetic flux by the rotor do not match each other in a case where the actual magnetic pole position of the rotor (permanent magnet) does not coincide with 0°. This rotation torque gives rise to rotation until the rotor matches the direction of the magnetic flux by the d-axis current Id. The magnetic poles of the rotor are drawn as a result to the d-axis current Id. This drawing ends once the magnetic pole position of the rotor match each other ultimately in the virtual d-axis (Yes in step S2). The magnetic pole position of the rotor reaches 0° at this point in time, and a counter value N1 of the magnetic pole position sensor (encoder) at this time is read (step S3).
Next, the rotor is rotated (step S4), and a rotation angle from the virtual d-axis until detection of an origin pulse of the encoder is detected as a counter value N2 (Yes in step S5, step S6). A difference Ndif between the counter value N2 at this time and the counter value N1 is worked out. This difference Ndif constitutes a value corresponding to the amount of deviation between the origin of the output signal of the encoder and the origin of the magnetic pole position of the rotor (step S7). Next, the difference Ndif is converted to a phase difference in electrical angle, and Ndif is multiplied by a conversion coefficient K, to work out a phase difference θdif (step S8). This phase difference θdif is stored in a memory, such that, every time that the origin pulse of the encoder is detected during normal operation of the permanent magnet-type synchronous motor, magnetic pole alignment is performed by adding the phase difference θdif to a detected magnetic pole position θ0, and the true magnetic pole position θ, corrected by the amount of deviation, is worked out, to be used in vector control (step S9).